The present invention relates to primers and in particular to primers employing a pair of pressure responsive devices.
In firing a weapon, usually a primer employing a primary propellant is initially ignited which in turn ignites a main charge. A primer is designed to be conveniently ignited by percussion or electrical ignition to produce an intensely hot expanding gas which efficiently ignites a main charge. Numerous types of primers are known, such as spark igniters, hypergolic igniters, bayonet primers, ball head primers etc.
If the main charge is a liquid propellant, it is important to isolate this liquid propellant so it does not wet the primary propellant. Such isolation is important because an intimate contact between the two propellants results in poor ignition. Poor ignition generally happens if the liquid propellant enters the primer since ignition must now commence over the relatively confined area within the primer.
A known primer houses the primary propellant and separates it from the main charge. This primer retains the primary propellant in a cylindrical cavity which is covered by a cylindrical piston. The primer has a plurality of radial orifices which are initially sealed by the piston before firing. Upon ignition of the primary propellant its expanding combustion gasses drive the piston away from the orifices thus allowing emission of the combustion gasses of the primary propellant through the orifices to ignite the main charge. A disadvantage with this piston arrangement is that the combustion gasses of the primary propellant are ejected almost immediately and at a moderately low pressure. As a result the flames from the primer are emitted somewhat randomly and at a pressure which is not especially conducive to efficient ignition of the main charge.
The present invention avoids such problems and provides unique advantages by employing a housing having a frangible seal upstream and a valve means downstream. As a result the primary propellant is contained for a brief interval by the valve means to allow fuller combustion. Upon reaching a predetermined pressure the combustion gasses of the primary propellant are released and bear upon the frangible seal. This frangible seal provides several functions. For the case where the main charge is a liquid propellant the seal prevents the liquid from flowing into the housing, thereby insuring that main charge is not ignited within the relatively confined area within the housing. Moreover, isolating the liquid propellant from the interior of the housing prevents the build-up of high pressure gasses that can unduly stress the housing. This latter feature is important for embodiments wherein the housing is reusable. Importantly, the frangible seal provides a high pressure restraining device which allows the primary propellant to rise to a relatively high and accurately repeatable pressure before the primary propellant is released to the main charge. This last feature insures an energetic expulsion of hot, highly pressured combustion gasses which efficiently and energetically ignite the main charge.
Accordingly, by employing such apparatus a main charge can be ignited without using erodable electrodes that require significant electrical energy. Furthermore, because a frangible seal is used, a high degree of isolation is achieved which avoids gaseous venting into a liquid propellant. Moreover, toxic chemicals such as hydrochloric acid are not required as with hypergolic ignition.
Another significant advantage is that the action of the primer is reproducible. This feature is important since projectiles must be consistently launched without significant variations in their range. Of course, any inconsistencies in muzzle velocity caused by inconsistencies in the primer, result in firing inaccuracies. Since the pressure at which the primer operates is reproducible and accurate, the rate of heat transfer to the liquid propellant is also accurate and reproducible. Such kinetics can be thus controlled and can be simulated by computer.